Functions at Edge

Functions at Edge (FaE) are lightweight serverless functions that execute at the edge locations of a content delivery network (CDN) like AWS CloudFront. These functions enable developers to execute code in proximity to end-users, and we can use these functions for several purposes:

• Implementing advanced HTTP logic: CloudFront offers native features like redirecting from HTTP to HTTPS and routing to different origins based on request paths. Edge functions extend CloudFront’s capabilities, enabling the implementation of advanced HTTP logic such as cache key normalization, URL rewriting, and HTTP CRUD operations.

• Reducing application latency: Offloading certain application logic from the origin to the edge leverages caching (e.g., A/B testing) and executes closer to users (e.g., HTTP redirections, URL shortening, HTML rendering). In microservices or micro-frontend architectures, edge functions centralize common logic (e.g., Authorization & Authentication) at the application entry point, streamlining development and reducing redundancy.

• Protecting the application perimeter: Edge functions enforce security controls like access control and advanced geoblocking at the edge, minimizing the attack surface of the origin and optimizing scalability.

• Request routing: Edge functions enable routing each HTTP request to specific origins based on application logic, facilitating scenarios such as advanced failover, origin load balancing, multi-region architectures, migrations, and application routing.

CloudFront offers two types of edge functions: CloudFront Functions and Lambda@Edge. CloudFront Functions offer sub-millisecond startup times and immediate scalability to handle millions of requests per second, making them ideal for lightweight tasks such as cache normalization, URL rewriting, request manipulation, and authorization.

On the other hand, Lambda@Edge extends AWS Lambda functionality, distributing execution across Regional Edge Caches. While Lambda@Edge provides more computing power and advanced features like external network calls, it has higher costs and latency overhead.

Lambda@Edge

Lambda@Edge is a powerful feature of CloudFront that enables the execution of lightweight Lambda functions at CloudFront edge locations. These functions provide dynamic capabilities to adjust traffic between viewers and origins, offering various opportunities for customization and optimization. However, due to the nature of edge computing, certain limitations must be considered. The cost for Lambda@Edge is $0.60 per 1 million requests.